The invention is generally directed to purification and to recovery of waste streams containing high alkali metal chloride levels ("waste brine stream") and to use of those waste brine streams in conventional chlor-alkali diaphragm cells.
Electrolytic production of chlorine and alkali metal hydroxide conventionally involves the electrolysis of aqueous solutions of an alkali metal chloride in cells equipped with diaphragms made entirely or largely of asbestos. Conventional asbestos diaphragms used in these cells generally have an on line lifetime of about twelve months in a commercial scale of electrolytic process.
For economic and environmental reasons, it is desirable to cycle aqueous alkali metal chloride containing industrial waste streams to electrolysis processes undertaken in conventional chlor-alkali cells.
In attempts to electrolyze certain high level alkali metal chloride containing waste streams, from other industrial processes, severe swelling and plugging of the asbestos diaphragm with attendant voltage increases and efficiency losses, occurred within days of the beginning of the operation. At each occurrence of this swelling and consequent plugging of the asbestos diaphragm, the cell operation had to be shut down to wash the asbestos diaphragm to free it of those substances which caused the swelling and consequent plugging.